No abstract

Partitioning of two non-ionic glycosides, 4-nitrophenyl-or-~-mannopyranoside and 4-nitrophenyl-N-acetyl-~-~-glucosaminide, in aqueous dextran-poly(ethy1ene glycol) and dextran-polyvinylpyrrolidone two-phase systems of different polymer concentrations and various ionic compositions has been studied. The differences in the abilities of the aqueous media in the coexisting phases of the systems used to participate in ionic and hydrophobic hydration interactions with a solute being partitioned have been estimated previously. The relative hydrophobicity of the solutes expressed in equivalent quantity of CH, groups depends on the composition of the aqueous medium (the nature and concentration of the salts present, the nature of the phase polymers). The difference between the relative hydrophobicities for the non-ionic solutes, however, is independent of the above factors. This indicates that the partition technique can be considered as an adequate general method for estimation of the relative hydrophobicity of solutes.

Acid-base equilibria of sulphonephthalein dyes, fluorescein and eosin, in aqueous solutions of several non-ionic polymers containing 0.01 or 0.05 mot dm-3 buffers have been studied as functions of the polymer concentration and the initial pa: of the buffer. Spectrophotometric and potentiometric data show that the paH in the polymer solution depends on the initial pa: of the buffer and on the type and concentration of polymer present in the solution.The general trend observed in aqueous solutions containing 0.01 mol dm-3 universal buffer was that for pa: < 5.5 the polymers examined decrease the acidity of the aqueous medium with an intensity dependent on their chemical nature and concentration. The polymers studied did not affect the pa: of the aqueous medium in paH range 5.57.5. At pa: > 7.5 the polymers decrease the basicity of the aqueous medium. The effects may be viewed as a shift of paH of the aqueous medium towards 7.0, the effect increasing with distance from 7.0. The results of studying acid-base and tautomeric equilibria of fluorescein and eosin in polymer solutions show that the equilibrium constants for the dyes change in reference to pure water. The changes determined are similar to those observed for the dyes in water-organic solvent mixtures.The acid-base equilibria of the dyes in the aqueous polymer solutions examined appear to change owing to polymer effects on the structure and/or state of water, leading to changes in the hydration and thermodynamic activity of both H+ and OH-ions. This view is supported by the data obtained in the study of solvatochromic effects of sulphonephthalein dyes in polymer solutions. The results obtained support the earlier suggestion that aqueous polymer solutions behave as water-like liquids of varied solvent properties.

The effect of salts KSCN, KI, KBr, KCI, KC104, KF, K2SO4 and NH4CI, LiC1, NaC1, KC1, CsC1 on the binodials of the phase diagrams for aqueous biphasic dextranpolyvinylpyrrolidone, dextran-polyvinyl alcohol, dextran-ficoll and dextran-polyethylene glycol systems was studied. It is established that the K-salts present at the concentrations of 0.1 and 0.5 mol/kg alter the binodials of the phase diagrams for the above systems. The effect of a salt is found to be related to the lyotropy of the salt quantified by the salt molal surface tension increment. It is assumed that phase separation in an aqueous polymer biphasic system is affected by the presence of a salt mainly due to the effect of the salt on the structure and/or state of water in the system.

Partition behavior of liposomes of different composition in the aqueous Ficoll-Dextran biphasic system was examined. The relative hydrophobicity of the liposomes was estimated. The effect of cholesterol on the solvent interactions of lecithin and sphingomyelin liposomes was studied. It is found that the effect of phosphatidylethanolamine on the hydrophobic character of lecithin liposomes exceeds that produced by cholesterol. The relative hydrophobicity of all the liposomes examined was found to be independent of the ionic composition of the system containing varied amounts of NaCl and Na-phosphate buffer, pH 7.4. The hydrophobic character of the liposomes under study is shown to increase in the following order: phosphatidylserine less than phosphatidylethanolamine less than phosphatidylcholine less than sphingomyelin. Hydrophobic properties of the liposomes are compared to those of human red cells. It is suggested that the dependence of the hydrophobic character of membrane particles on the ionic composition of an aqueous environment can be of fundamental importance for the selective distribution of the particles in vivo.